Polycarbosilane is widely used as a precursor for producing SiC-based continuous fiber primarily or as a precursor of SiC coating, SiC powder, and SiC composite materials for improving their acid and heat resistance.
As a method of producing the polycarbosilane that is widely used for producing SiC-based fiber or as SiC coating precursor, the Yajima (refer to U.S. Pat. No. 4,052,430) method by means of high-temperature pressurized reaction above 400° C., which uses polydimethylsilane as a starting material, is primarily used at present. According to this method, however, pyrolytic by-products such Me2SiH2, Me3SiH etc. are created during the reaction as it is pressurized by a pressure cooker, thereby rising internal pressure of the pressure cooker above 100 atm during the reaction; in particular, due to ignition property of these silane-based gases in the existence of oxygen at low temperature, there exists a problem in stability due to a danger of ignition when these gases are leaked by the pressurization during the reaction.
In order to solve this problem, polycarbosilane was composed using polyborodiphenylsiloxane as catalyst at atmospheric pressure by Yajima (refer to Nature Vol. 273 No. 15, 525–527), thereafter, it was reported by Kurosaki Refractories Co. Ltd. that polycarbosilane was composed using solid acids such as AlCl3, ZrCl2, VCl3, SbCl3 as catalyst (refer to U.S. Pat. No. 4,590,253, Japanese Patent JP 87-79228) within the range of 320° C.˜370° C. However, it is difficult to control acidity of the catalyst since these solid catalysts showed strongly acid, and the yield of final products was low and also it is difficult to control molecular weight of these products.